Question

An investigation was carried out to determine which of three antibacterial soaps is most effective. Four petri dishes labeled A, B, C, and D were set up. The same amount and type of bacteria was added to each dish. Next, 2 mL of a different brand of soap were added to dishes B, C, and D. Then, 2 mL of water were added to dish A, instead of soap. The dishes were incubated at 37°C for 24 hours. At the end of the investigation, the amount of bacteria in each dish was determined. Dish D had the least bacteria. It was concluded that the soap in dish D was the most effective soap to use against bacteria. Which statement best describes the validity of this conclusion? The conclusion is not valid since the same amount of bacteria was used in each dish. The conclusion is valid since too small a sample of bacteria was used in this investigation. The conclusion is valid since the amounts of bacteria were measured at the end of the investigation. The conclusion might not be valid since the investigation was carried out only once.

Answer 1

The conclusion is NOT valid since too small a sample of bacteria was used in this investigation. 

NOT:
 The conclusion is not valid since the same amount of bacteria was used in each dish.
The conclusion is valid since too small a sample of bacteria was used in this investigation.
The conclusion is valid since the amounts of bacteria were measured at the end of the investigation.
The conclusion might not be valid since the investigation was carried out only once.